1. Field of the Invention
This invention relates to a display panel control device which generates driving signals for a display panel and to a display apparatus having the above control device, and in particular relates to a display panel control device capable of reducing the capacity of the frame memory and a display apparatus having such a control device.
2. Description of the Related Art
Liquid crystal displays, which are one type of display, are coming into widespread use as space-saving display devices. In recent years, they are also coming to be used as display devices for display of video. Liquid crystal display panels have source lines, to which are applied display driving voltages corresponding to a image data for a current frame; gate lines, which are driven with scan timing; and cell transistors and pixel electrodes, placed at a positions of intersection of the above lines. Display driving voltages are applied to a liquid crystal layer across pixel electrodes via a cell transistor to cause changes in a transmittance of the liquid crystal layer, in order to display the desired image.
In general a response characteristics of liquid crystal materials are not satisfactory; there are cases in which, depending on a state of a previous frame, it is not possible to change to a state corresponding to a input grayscale data within a interval of a single frame, and such poor response characteristics may result in degraded video display quality. In order to mitigate such slow response characteristics, driving compensation methods have been proposed in Japanese Patent Laid-open No. 2002-297104(corresponding to U.S. Patent Laid-open US-2002-0140652-A1), Japanese Patent Laid-open No. 2002-6285, and Japanese Patent Laid-open No. 2002-202763.
This driving compensation method, put simply, is a method in which a display driving data for a current frame is generated based on a previous-frame display data and a current-frame display data, and the display panel is driven using this display driving data. Thus by referencing the display data for the previous frame, the display driving data can be generated which takes into account the state of the previous frame.
In Japanese Patent Laid-open No. 2002-297104, a method is described in which a compensation value corresponding to a combination of a post driving state data for the previous frame and the current-frame display data is added to or subtracted from current-frame display data to calculate display driving data for the display data of the current frame. Further, driving at the display driving voltage corresponding to the display driving data does not necessarily result in a liquid crystal layer state corresponding to the display driving data, and so the method is described in which the difference value corresponding to the combination of the post driving state data for the previous frame and the current-frame display data is added to or subtracted from the current-frame display data, the post driving state data is calculated, and the result is stored in frame memory.
As described above, in order to drive a liquid crystal display panel using a driving compensation or other method, the supplied display data for the current frame (or the post driving state data for the current frame to be generated, or other current frame data) is stored in frame memory, and the display driving data for the current frame must be generated from a relation between the display data for the previous frame stored in frame memory (or, the post driving state data or other previous frame data) and the current-frame display data. To this end, the frame memory must store, at least, display data for the previous frame (or the post driving state data, or other previous-frame data) and current-frame display data (or the post driving state data, or other current-frame data), so that large-capacity frame memory is required, and there is the problem of increased costs.